The invention herein described was made in the course of or under a contract thereunder with the United States Air Force Systems Command.
This invention generally relates to a process for the dimerization of norbornadiene. In particular, the invention relates to producing a hydrocarbon mixture having a high concentration of a monoolefinic hexacyclic hydrocarbon known by the systematic chemical name of exo-exo stereoisomer of hexacyclo( 7.2.1.0.sup.2,8 0.1.sup.3.7 0.1.sup.5.13 0.0.sup.4,6)tetradec-10-ene, (also designated as hexacyclo[9.2.1.0.sup.2,10 0.0.sup.3,8 0.0.sup.4,6 0.0.sup.5,9 ]tetradec-12-ene). The stereoisomer results from the catalytic dimerization of norbornadiene which is a C.sub.7 H.sub.8 bicyclic, diolefinic hydrocarbon. More particularly, the invention relates to a process for producing a mixture of a high concentration of the exo-exo form of the hexacyclic dimer. The latter is a C.sub.14 H.sub.16, six-ring monoolefinic hydrocarbon. The process can be continuous and has an advantage of recycling certain streams thereby reducing costs and increasing yields. Also, the invention relates to a process in which the product has been hydrogenated to convert the monoolefinic hexacyclics into completely saturated hexacyclics. Hydrogenation of monoolefinic hexacyclic dimer to the saturated dimer improves stability of the product towards oxidation thereby enhancing its utility as a high energy fuel. Completely saturated exo-exo hexacyclic dimer has utility as a component of high energy fuel.
An object of the present invention is to provide an economical process which can produce a composition which has a maximum concentration of hexacyclic norbornadiene dimers and a minimal concentration of pentacyclic norbornadiene dimers and other compounds. Also, the composition can be used as a component of a high energy fuel for use in either jet or rocket propulsion. Jet propulsion includes a jet engine which can be used for missile, plane and others and includes the three basic types, i.e., ramjet, turbo-jet and pulse jet. The term jet generally refers to a device requiring air whereas rocket generally refers to a device containing its own oxygen or oxidizing agent.
Norbornadiene is also known as bicyclo( 2.2.1)-heptadiene-2,5. A method of preparation is disclosed in U.S. Pat. 2,875,256 issued Feb. 24, 1959. Norbornadiene is referred to as NBD hereinafter. NBD can be represented by either one of the following structural formulas: ##STR1##
Dimerization of NBD is disclosed in U.S. Pat. No. 3,377,398, issued Apr. 9, 1968. The disclosed process results in the production of various dimer mixtures. The process therein involves the use of an iron catalyst system, e.g., ferric acetylacetonate and tirethylaluminum, and a temperature above 140.degree. C. The product of said method is a mixture which includes both the monoolefinic hexacyclic and diolefinic pentacyclic dimers.
U.S. Pat. No. 3,282,663, issued Nov. 1, 1966, discloses the dimerization of NBD to both pentacyclic and hexacyclic dimers. In one example, tetrakis(triphenylphosphino)nickel is the catalyst, in another, iron acetylacetonate and triethylaluminum is the catalyst system. Use of cobalt acetylacetonate is suggested.
U.S. Pat. No. 3,326,992, issued June 20, 1967, discloses the partial hydrogenation of NBD dimer mixtures.
U.S. Pat. No. 3,326,993, issued June 20, 1967, discloses the dimerization of NBD, in the presence of a certain cobaltcontaining carbonyl catalyst, to heptacyclic dimers. The resulting dimer mixture contains major proportions of the completely saturated dimer.
U.S. Pat. No. 3,329,732, issued July 4, 1967, discloses an improved method for the dimerization of NBD. The catalyst comprises certain metal salts of the tetracarbonylcobaltate anion wherein the metal is zinc, cadmium, mercury or indium. Resulting dimer mixture contains predominantly hexacyclic dimers.
Catalytic reaction of NBD and butadiene is disclosed in an article in The Journal of Organic Chemistry, January, 1970, Vol. 35, title, "Catalytic Norbornadiene-Butadiene and Norbornadiene-1,1-Dimethylallene Codimerization", by A. Greco, et al., pages 271-274. One of the disclosed catalysts is a three component system of tris(acetylacetonate)Iron-AlEt.sub.2 Cl-bis(diphenylphosphino)ethane. AlEt.sub.2 Cl refers to diethylaluminum chloride. One of the dimers reported therein, i.e., FIG. 1e, has been identified as the exo-exo stereoisomer of hexacyclic dimer of norbornadiene.
Also, a catalytic reaction of NBD is disclosed in an article in The Journal of the American Chemical Society, Vol. 94, July 26, 1972, starting page 5446, titled, "Dimerization and Trimerization of Norbornadiene by Soluble Rhodium Catalyst", by Nancy Acton et al. This article discloses the exo-exo form of the hexacyclic dimer of NBD.
As the previous discussion indicates, many NBD dimers are possible. G. N. Schrauzer, in his review "On Transition Metal-Catalyzed Reactions of Norbornadiene and the Concept of a Complex Multicenter Processes" in Advances on Catalysis 18, 373 (1968) Acad. Press, describes the fourteen theoretically possible dimers of NBD.
Thus the process problem in the dimerization of NDB, as can be visualized from the number of possible isomers is to obtain substantial amounts of the exo-exo isomer at high yields and at reduced costs. Also, the problem is to minimize the production of pentacyclics. The latter are not desirable as high energy fuels because of their high melting points. Separation of pentacyclics from the hexacyclics is commercially not feasible. On the other hand, the exo-exo hexacyclic dimer can be easily separated from small amounts of unreacted feed and other products, particularly higher boiling polymers. Hydrogenation of the exo-exo material provides a material which can be used as a component for high energy, high density fuel.
The advantages of the present invention are many. The process can be continuous. Recycling of various streams, without build up of unwanted products, within the process reduces costs and increases yields.